1. Field of the Invention
The invention relates to new aqueous polyester-polyurethane dispersions, to coating compositions comprising these dispersions and to the coating materials prepared therefrom.
2. Description of the Prior Art
Ionically modified polyurethane dispersions and their aqueous formulations are known prior art. One important field of use of aqueous formulations of ionically modified polyurethanes lies in the area of the coating of plastics components.
For years the efforts at weight saving in the passenger car have gone hand in hand with increased use of plastic, in the interior as well. Because of aesthetic and technical requirements, plastics components in the car are normally coated, in order to protect the plastic against external influences, such as sunlight, chemical, thermal and mechanical exposure, in order to obtain certain shades and colour effects, in order to mask defects in the plastic surface or in order to give the plastic surface a pleasant feel (tactility). In order to enhance the tactile properties of plastics components in the car interior, use has been made increasingly in recent years of what are called soft feel coating materials. “Soft feel effect” for the purposes of the present invention denotes a particular tactual sensation (tactility) of the coated surface. This tactility can be described using terms such as velvety, soft, rubber-like or warm, whereas, for example, the surface of a painted car body or else an unpainted polymer sheet or one coated with a customary clearcoat or topcoat material and made, for example, of ABS, Makrolon® (polycarbonate, Bayer AG) or plexiglass feels cold and smooth.
In tune with the trend of avoiding solvent emissions to the environment, recent years have seen the establishment of aqueous soft feel coating materials based on the polyurethane chemistry, as disclosed, by way of example, in DE-A1 44 06 159. As well as an excellent soft feel effect, these coating materials also produce coatings having good resistance and protective effect for the plastics substrate.
It has since been found, however, that even these coating materials do not have adequate adhesion to numerous plastics substrates. In order to remove this drawback, the coating system on high-grade plastics parts according to the present prior art is effected with two or three coats. A coating system of this kind is composed of primer, optionally a basecoat and a topcoat. The primer in this system takes on the function of the adhesion promoter between substrate and coating material.
Accordingly, within the field of the coating of plastics components, there is a demand for products which have not only good soft feel properties but also good adhesion to the substrates. These products can then be used without a primer in a single-coat system.
DE-A1 2 651 506 discloses a process for preparing water-dispersible polyurethanes. The products of this process, however, are unsuitable for use as a single-coat soft feel coating material for plastics components, since they lack the necessary adhesion properties.
Likewise, soft feel coating materials are described in DE-A1 44 06 159. Therein, however, satisfactory adhesion properties of the coating films are not obtained.
The teaching of DE-A1 101 38 765 discloses that the use of polyethers prepared starting from aromatic diols in aqueous polyurethane (PU) dispersions leads to products which in view of their improved adhesion to a variety of substrates are suitable as priming binders. Because of their inadequate tactility, however, the products are not suitable for use as soft feel coating materials.
An object of the present invention was to provide aqueous polyurethane dispersions which have suitability as soft feel coating materials and at the same time have excellent adhesion to plastics substrates.